Advancements continue to be made in wireless communications technology. For example, wireless local area networks (WLANs) and wireless personal area networks (WPANs) networks are becoming more common in homes and businesses. Such networks may include a variety of independent wireless electronic devices or terminals, which wirelessly communicate with one another. WLANs and WPANs may operate according to a number of different available standards, including IEEE standards 802.11 (Wi-Fi), 802.15 (Bluetooth) and 802.16 (WiMax), as well as the WiMedia Alliance Ultra-Wideband (UWB) standard.
FIG. 1 is a block diagram showing a conventional wireless network 100, including multiple terminals configured to communicate with one another over exemplary WPAN 125. The wireless terminals may include any electronic devices or nodes configured to communicate with one another. For example, FIG. 1 depicts a home network in which the electronic devices include a personal computer 120, a digital television set 121, a digital camera 122 and a personal digital assistant (PDA) 123. The network 100 may also include an interface to other networks, such as modem 130, to provide connectivity of all or some of the wireless devices 120-123 to the Internet 140, for example. Of course, there are many other types of wireless networks in which electronic devices communicate with one anther, including networks in manufacturing plants, medical facilities, security systems, and the like.
Wireless devices may communicate with one another using directional antennas, which may be fixed or steerable, for extending transmission range. For example, recent wireless networks (e.g., WiMedia wireless USB) operate in very high frequency bands (e.g., 60 GHz), and thus use directional antennas to compensate for high path loss associated with high frequency bands. In both centralized and distributed wireless networks, wireless devices using directional antennas must align their respective antennas at the same time in order to communicate. In other words, the wireless devices must first find each other. When the wireless devices have steerable directional antennas, this may be accomplished by simultaneously scanning (e.g., sweeping their antenna beams) around surrounding areas. The wireless devices may not discover one another unless there is pre-coordination among them to assure that they are sweeping their antenna beams at the same time. When the wireless devices have fixed directional antennas, they will discover only those devices located within the fixed antenna beam.
Beacons are widely used to convey important control information between devices. Beacons are usually broadcast so that all devices in the transmission range of the beaconing device can receive the beacons. For example, an IEEE 802.11 access point periodically sends out beacons so that the IEEE 802.11 wireless devices around the access point can associate with the access point and communicate. As stated above, in wireless networks in which directional antennas are used, beacons may only be sent in certain directions. As a result, only a limited number of devices in proximity of the beaconing device will receive the beacons. The wireless devices may be pre-programmed to know the direction of each other's antennas, but this requires a protocol to coordinate the wireless devises' antenna directivity, as well as beacon transmission, reception and processing.
In other words, wireless devices may not be able to discover and communicate with each other even though they are in the same network 100 and in proximity to one another. Such coordination or synchronization is difficult and costly to implement. However, wireless devices not having a common time-domain reference point for coordinating antenna control and/or beacon transmission will not communicate properly as a network.
Furthermore, wireless devices in proximity with one another may not necessarily be able to communicate, depending on their relative locations and the directional capabilities of their antennas. This is especially true for wireless devices having fixed directional antennas. Accordingly, a situation may arise in which wireless devices in a wireless network (e.g., network 125) form multiple, independent beacon groups, each of which includes one or more of the wireless devices.
Such beacon groups are unsynchronized and not able to directly communicate with one another. For example, if two wireless devices having fixed directional antennas are not located within one another's antenna sectors, the two wireless devices necessarily form two separate beacon groups. A third wireless device, e.g., with a steerable directional antenna, may be able to communicate with both beacon groups. However, the third wireless device must choose one of the beacon groups to join, or decide to join both beacon groups, in which case it must send two beacons, possibly in different antenna sectors. Sending two beacons, however, perpetuates the unsynchronized beacon groups, thus wasting medium time and potentially causing interference.
Accordingly, it would be desirable to provide wireless devices and a method of wireless communications that provide a mechanism enabling wireless devices to find and communicate with each other, using a single synchronized beacon group, particularly when the wireless devices are using fixed directional antenna systems.
In accordance with a representative embodiment, a method of merging a plurality of unsynchronized beacon groups in a wireless network, each beacon group comprising at least one wireless device, comprises:
receiving a first beacon from at least one first wireless device in a first beacon group, the first wireless device having a first directional antenna;
receiving a second beacon from at least one second wireless device in a second beacon group that is not synchronized with the first beacon group, the second wireless device having a second directional antenna; and
relocating a first response beacon and sending the relocated first response beacon to the first wireless device in the first beacon group, the relocated first response beacon instructing the first wireless device to relocate the first beacon, wherein the second beacon, the relocated first response beacon, and the relocated first beacon are synchronized.
In accordance with another representative embodiment, an apparatus configured to merge a plurality of unsynchronized beacon groups in a wireless network, each beacon group comprising at least one wireless device includes:
a transceiver configured to receive a first beacon from at least one first wireless device in a first beacon group, the first wireless device having a first directional antenna, and to receive a second beacon from at least one second wireless device in a second beacon group that is not synchronized with the first beacon group, the second wireless device having a second directional antenna; and
a processor configured to synchronize a timing of a first response beacon, responsive to the first beacon, with a timing of the second beacon by relocating the first response beacon, wherein the transceiver sends the relocated first response beacon to the first wireless device in the first beacon group, the relocated first response beacon informing the first wireless device to synchronize a timing of the first beacon with the timing of the second beacon by relocating the first beacon.